Mol Zr Research Articles

Preparation and spectroscopic characterisation of intercalation compounds of α-zirconium phosphate with Rhodamine B

The addition of increasing volumes of 10−2 M Rhodamine chloride solution to colloidal dispersions of α-zirconium phosphate exfoliated with n-propylamine induces flocculation of the layered compound, accompanied by ion exchange of the dye for the propylammonium cation, to give two intercalation compounds containing 0.19 and 0.66 mol of Rhodamine per mol of Zr, and having interlayer distances of 1.9 and 2.47 nm, respectively. Excitation and emission spectra of the intercalation compounds showed a relevant blue-shift (15 nm) of the typical emission maximum of solid Rhodamine B, centred at 690 nm. The accommodation of guest molecules in the layered host is also discussed, on the basis of experimental data and computer simulation.

Silica-supported zirconocene catalysts: Preparation, characterization and activity in ethylene polymerization

Supported catalysts for ethylene polymerization have been prepared by interaction of Cp 2ZrX 2 (Cp= η 5-C 5H 5, X=Cl or CH 3) with silica chemically modified by (CH 3) 3SiCl (TMCS) or trialkylaluminium compounds AlR 3 (R=C 2H 5 (TEA) and i C 4H 9 (TIBA)). The interactions between the modificators and the silica surface have been examined by 1 H solid-state MAS NMR spectroscopy, DRIFTS and chemical analysis. The Cp 2Zr(CH 3) 2/SiO 2–TMCS catalyst showed a fairly high activity in ethylene polymerization (30–300 kg PE(mol Zr·h·bar) −1) even in the absence of any cocatalysts specially added. The addition of the cocatalyst (MAO or TIBA) led to a further increase in the activity of the supported catalysts. Polyethylene obtained with the Cp 2Zr(CH 3) 2/SiO 2–TMCS catalyst without any cocatalyst consisted of uniform polymer particles of a spherical shape replicating that of the silica particles, whereas the shapeless aggregates of finely dispersed polymer particles similar to those usually obtained with homogeneous systems were produced with the same supported catalyst in the presence of the MAO cocatalyst.

Synthesis, structure, and catalytic properties of ansa-Zirconocenes, Me 2X(Cp)(RInd) ZrCl 2 (X = C, Si; R = 2- p- or 3- p-tolyl)

ansa-Zirconocenes, Me 2X(Cp)(3-Tollnd)ZrCl 2 [X = C ( 7), Si ( 8); Cp = η 5-C 5H 5; Tol = p-C 6H 4CH 3] and Me 2Si(Cp)(2-TolInd)ZrCl 2 ( 9), have been prepared by the reactions of ZrCl 4 with the corresponding dilithiated ligands in diethyl ether at −78°C. The molecular structure of complex 9 has been determined by a single crystal X-ray diffraction study. Propylene polymerization has been studied for complexes 7, 8 and 9 in the presence of methylaluminoxane (MAO). Complex 9 reveals the highest catalytic activity of 1570kg PP/(mol Zr h atm) and the highest molecular weight of 1.2 × 10 6 among the three catalysts. Complex 9 produces atactic polypropylene (PP), whereas 7 and 8 afford PP with a weak syndiotacticity at low temperature.

Full and partial polarization switching characteristics of sol-gel derived Pb(ZrxTi1-x)O3 thin films

In this study, polarization switching characteristics of Pb(Zr x Ti1-x )O3 (PZT) thin films were investigated. Switching times (t s) were found to be decreased as the Zr mol% was increased. But, the switching peak currents (I max) showed the largest value at 50 mol% Zr. As a result of this experiment, t s was found to be depended on the remanent polarization and coercive field and also I max strongly depended on the dielectric constant of PZT thin films. In order to investigate the partial switching kinetics of PZT thin films, short and relatively small voltage pulses were applied to the MFM (metal-ferroelectric-metal) PZT capacitors and polarization switching curves were measured with a variation of the total width of the applied pulses. Also, the switching curves were measured at different applied voltages (4, 8, 10, 12 and 14 V). As the applied voltages increased t s and I max were found to be decreased and increased, respectively. In case of fatigued specimen which we applied ± 10 V square pulse for 1010 cycles, t s and I max were found to be shorter and smaller than those of virgin specimens. This is due to the decrease of the remanent polarization and the increase of the coercive field.

Syndiospecific propene polymerization with polymer-supported metallocene catalyst

Copolymers of styrene and a styrene derivative having a C s symmetrical ligand moiety were synthesized and used as the carrier for the synthesis of supported-type zirconocene catalysts. Propene polymerization was conducted using the resulting catalyst together with methylalumoxane (MAO), which gave syndiotactic polypropene. The productivity of the polymer-supported catalyst (4010 kg PP (mol Zr) −1 for 24 h) was, however, very low compared to that of the corresponding homogeneous catalyst (9130 kg PP (mol Zr) −1 for 20 min).

Heptane‐soluble homogeneous zirconocene catalyst: Synthesis of a single diastereomer, polymerization catalysis, and effect of silica supports

AbstractBis(1‐indenyl)‐di[1′S, 2′R, 5′S)‐methoxy]silane (1) was converted into a mixture of corresponding ansa‐diastereomeric zirconocenes. Further purification afforded a single dia‐stereomer, di[(1′S, 2′R, 5′S)‐methoxy] silylene‐bis[η5‐1(R, R)‐(+)‐indenyl] dichlorozirconium (2), which is optically active and hydrocarbon soluble. Extremely rapid ethylene, propylene, and ethylene‐hexene polymerizations were observed both in toluene and n‐heptane solutions; for instance, at 50°C, activity for ethylene polymerization reaches ∼ 1.5×1010 (g of PE/((mol of Zr) · [C2H4] · h). The “bare” zirconocenium ion generated from 2/TIBA/Ph3CB(C6F5)4 exhibits unusual polymerization behaviors; the polymerization activity increases monotonically with temperature of polymerization (Tp) up to a conventional polymerization condition (50–70°C), and the 13C NMR study shows that the isotactic poly‐propylene obtained has fairly high [mmmm] methyl pentad distributions at high Tp (⩽25°C with [mmmm] ∼ 0.93–0.75) and a perfect stereoregularity at low Tp (⩽0°C with [mmmm] > 0.99). The catalyst precursors 2 and Et(Ind)2ZrCl2 (3) supported on silica by different approaches produced poly(olefins) of different molecular weights and stereoregularities, and a methylaluminokane and Ph3CB(C6F5)4 free silica‐supported zirconocene system was found to be activated by triisobutylaluminum. © 1995 John Wiley & Sons, Inc.

C2v- and C2-Symmetric ansa-Bis(fluorenyl)zirconocene Catalysts: Synthesis and .alpha.-Olefin Polymerization Catalysis

c 2υ -symmetric ethylenebis(9-fluorenyl)zirconium dichloride (1) and its C 2 -symmetric bis[9-(1-methyl)fluorenyl] derivative (2) have been synthesized in good yields using a convenient synthetic route. Precursor 1 activated with triphenylcarbenium tetrakis(pentafluorophenyl)borate (3) catalyzes propylene polymerization with a constant activity of (6.28 ± 1.63) x 10 7 g of PP/((mol of Zr).[C 3 H 6 ].h) between -20 and +70 °C. The polypropylene is ideally atactic and has the same M w of (6.03 ± 1.19) x 10 5 . The above system catalyzes ethylene polymerization with a maximum activity of 1.4 x 10 10 g of PE/((mol of Zr).[C 2 H 4 ].h) at -20 °C which decreases exponentially with an increase of T p . All the polyethylenes produced between -20 and +50 °C have the same M w of (5.57 ± 0.49) x 10 5 . In contrast, precursor 2 catalyzed the formation of anisotactic polypropylene of low stereoregularity. Molecular mechanics calculations indicated that substituents on the fluorenyl rings have little effect on both diastereomeric ratios in the synthesis and stereoselectivities in the polymerization.

Silolene‐Bridged zirconocenium polymerization catalysts

AbstractA new silolene‐bridged compound, racemic (1,4‐butanediyl) silylene‐bis (1‐η5‐in‐denyl) dichlorozirconium (1) was synthesized by reacting ZrCl4 with C4H8Si (IndLi)2 in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta‐fluorophenyl) borate (2) to produce in situ the zirconocenium ion (1+). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (Tp = −55°C), producing refluxing n‐heptane insoluble isotactic poly(propylene) (i‐PP) with a yield of 99.4%, Tm = 164.3°C, δHf = 20.22 cal/g and M̄w = 350 000. It has catalytic activities of 107−108 g PP/(mol Zr · [C3H6] · h) in propylene polymerization at the Tp ranging from −55°C to 70°C, and 108 polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1+ decreases gradually as Tp approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1+ is more stereospecific than the analogous cation derived from rac‐dimethylsilylenebis (1‐η5‐indenyl)dichlorozirconium (4). The variations of polymerization activities in ethylene and in propylene for Tp from −55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium‐propylene π‐complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π‐complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude rE ˜ 4rp. Furthermore, rE.rp ˜ 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo‐selectivity than the corresponding 1+ or 4+ system. © 1994 John Wiley & Sons, Inc.

Low‐temperature isospecific polymerization of propylene catalyzed by alkylzirconocene‐type ‘cations’

AbstractThe rac‐ethylenebis(indenyl)methylzirconium ‘cation’ (1), generated from rac‐Et(Ind)2ZrMe2 and Ph3CB(C6F5)4, has recently been shown to be exceedingly active and stereoselective in propylene polymerization. The ethyl analog (2) can be produced by an alternate, efficient route involving a reaction between rac‐Et(Ind)2ZrCl2 and AlEt3 (TEA), followed by addition of Ph3CB(C6F5)4. The use of excess AlEt3 serves both to alkylate the zirconium complex as well as to scavenge the system. The propylene polymerization activity of the ‘cation’ 2 is about 7000 times greater than the activity of rac‐Et(Ind)2ZrCl2/methylaluminoxane (MAO) at Tp=−20°C. The related catalyst system rac‐Me2Si(Ind)2ZrCl2/TEA/Ph3CB(C6F5)4 (3) was found to produce 98.3% i‐PP with Tm 156.3°C and an activity of 1.8 × 109 g PP {(mol Zr) [C3H6]h}−1.

Zirconocenium cation catalysis of propene polymerization

Abstractrac‐Ethylenebis(1‐η5‐indenyl)dimethylzirconium (1) was reacted with triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) to produce in situ the rac‐ethylenebis(indenyl)methylzirconium cation (3). This aluminium‐free catalyst showed propene polymerization activity (A) and stereoselectivity which both increase with the decrease of polymerization temperature (Tp). At very low Tp, 3 behaved as a “single‐site” catalyst. An efficient way to produce such cation is to react ansa‐zirconocene dichloride with 2 in the presence of TEA (=triethylaluminium). A superior cationic catalyst was obtained from rac‐dimethylsilylenebis(1‐η5‐indenyl)dichlorozirconium, 2, and TEA, which polymerizes propene at −20°C(−55°C) with activity of 2×109 (3×108) g polypropene per (mol Zr η mol C3H6 η h) to polypropenes which are 93.8% (99.4%) isotactic with melting temperature Tm = 152.6°C (159.9°C) and viscosity‐average molecular weight Mv = 1.4×105 (2.2×105). The addition of methylaluminoxane lowers the A of the cationic catalyst especially at low Tp. Rigorously speaking, the cation derived from 1 or 3 behaves as a “single site” catalyst only at very low Tp. The use of TEA significantly and unexpectedly enhances the efficiency of the zirconocenium catalyst system.

Quantification of the influence of steric and electronic parameters on the ethylene polymerisation activity of (CpR) 2ZrCl 2/ethylaluminoxane Ziegler—Natta catalysts

Investigation of the effect of varying a cyclopentadienyl monoalkyl ring substituent, R (R  H, Me, Et, i-Pr, t-Bu, SiMe 3 and CMe 2Ph), on the catalytic behaviour of (CpR) 2ZrCl 2/ ethylaluminoxane for the ethylene polymerisation reaction was carried out. The activity data obtained can be explained by a quantitative combination of steric (cone angle, θ) and electronic (Hammett function, H) parameters. When θ is defined from the metal as apex, the activity is related to θ and H by the equation: Activity (× 10 5 g PE (mol Zr) −1h −1) = 0.040(θ 1) −84.44( F) ( R 2 = 0.91). A correlation of the degree of polymer branching, (determined from the polymer melting point via A = 13.1 − 0.097 ( T m)), with the electronic parameters only was also observed, viz. A = 3.1(σ m + 0.29 ( R 2 = 0.90). The activity of the catalytic system increases with increasing size of the R substituents as well as with increasing electron-donating ability of the substituents.

Olefin copolymerization with metallocene catalysts. I. Comparison of catalysts

AbstractA number of metallocene/methylaluminoxane (MAO) catalysts have been compared for ethylene/propylene copolymerizations to find relationship between the polymerization activities, copolymer structures, and copolymerization reactivity ratio with the catalyst structures. Stereorigid racemic ethylene bis (indenyl) zirconium dichloride and the tetrahydro derivative exhibit very high activity of 10 7 g (mol Zr h bar)−1, giving copolymers having comonomer compositions about the same as the feed compositions, molecular weights increasing with the increase of ethylene in the feed, random incorporation of comonomers, and narrow molecular weight distribution indicative of a single catalytic species. Nonbridged bis (indenyl) zirconium behaved differently, favoring the incorporation of ethylene over propylene, producing copolymers whose molecular weight decreases with the increase of ethylene in the feed, broad molecular weight distribution, and a methanol soluble fraction. This catalyst system contains two or more active species. Simple methallocene catalysts have much lower polymerization activities. CpTiCl2/MAO produced copolymers with tendency toward alternation, whereas Cp2HfCl2/MAO gave copolymer containing short blocks of monomers.